My thinking is backward from yours, Chuck. I think of the gel coat as the
layer that is supposed to be waterproof. The laminate may or may not be
waterproof depending on how well the layers are saturated with resin. I'm
sure if you scrape the gelcoat off something like a BayRay or other mass
produced boat, you will have a leak.
JIMinFL
wrote in message
oups.com...

JIMinFL wrote:
Don't sand thru the gelcoat if you don't have to, Chuck. Fiberglass isn't
waterproof without it. Patch the ground out blisters with Marine Tex or
other waterproofing filler.
JIMinFL

I don't know how you would fix a blister without removing the deformed
gelcoat.

Gelcoat ( essentially a layer of tinted resin) is somewhat porous. You
may be thinking of a barrier coat, not the gelcoat. When the term
"osmotic blister" is applied, the osmosis is the passage of water
through the gelcoat, not through the laminate. Plastic doesn't absorb
water, so if there are no voids in an FRP hull it isn't ever going to
become "waterlogged".

When I refer to "fairing", that's the same process you describe above
with the filler.

Happy New Year